The Transportation Security Administration (TSA) said Thursday that 4,239 firearms were found in carry-on bags coming through airport checkpoints in the United States last year, an increase of about 7 percent over the number found in 2017.

Nearly 9 out of every 10 of those firearms were loaded, and more than a third had a round chambered. TSA agents at Norfolk International Airport in Virginia also had the distinction of more than doubling its haul, as the number found there rose to 21, compared with 10 the year before.

The ever-rising tally of firearms is in line with record numbers of passengers and more jurisdictions allowing people to carry firearms openly or concealed — but it also makes one wonder how many have slipped by. A gun went all the way to Tokyo aboard a Delta flight from Hartsfield-Jackson International Airport in Atlanta last month.

Lisa Farbstein, a TSA spokeswoman, said Thursday that the agency has no way of estimating how many might be missed as the number of firearms at checkpoints continues to rise. (She also said yet another firearm had been found in a carry-on Thursday at Dulles International Airport but didn’t immediately have more details.)

A TSA agent checks passengers' luggage on a scanner at a security checkpoint at LaGuardia Airport in New York on Jan. 31. (Carlo Allegri/Reuters)

As is usually the case, the airports with the most firearms seizures were also among the busiest and in areas such as the South and the West, where rates of gun ownership are highest. Last year, the top five were Atlanta (298); Dallas/Fort Worth International (219); Phoenix Sky Harbor International (129); Denver International (126); and Orlando International (123).

Failing to properly stow firearms in checked bags and declare them, as required by law, not only creates a potential hazard at checkpoints but also disrupts the screening process, which can cause delays, TSA officials say.

Violators can face criminal and civil penalties. In 2017, the agency levied civil penalties of about $1.45 million against travelers who violated firearms laws at airports, according to records obtained through the Freedom of Information Act. Despite its weekly and annual roundups and warnings, however, the agency has declined to identify violators in most cases, citing privacy concerns.